Frequency modulation of ultrashort pulses emitted by Q-switched YAG:Nd lasers with active mode locking

An experimental investigation was made of frequency modulation (chirp) of the output radiation from continuously pumped YAG:Nd lasers operating under conditions of simultaneous Q switching and active mode locking. Chirp of the output radiation was first studied (in the absence of intracavity second harmonic generation) when it was due to phase self-modulation in intracavity components. It was demonstrated for the first time that chirp in lasers with intracavity second-harmonic generation could be controlled in respect of its amplitude and sign, and it appeared when a nonlinear crystal was tilted away from the phase-matching condition. Data were obtained for chirp of the output radiation of lasers with intracavity second-harmonic generation in LiIO₃ and KTP crystals, used as intracavity frequency doublers.